1. Field of the Invention
The present invention generally relates to the cyclic diol-derived blocked mercaptofunctional silane compositions, processes for their preparation, and rubber compositions comprising same.
2. Description of Related Art
A number of ether-based diol derivatives of sulfur silanes are known in the art that suffer from a tendency to yield bridged structures in favor of cyclic structures exclusively or primarily, leading to high viscosities and gellation, which limits their usefulness in elastomer manufacture. These silanes and their use further suffer from the hazards associated with the use of ethers, which have a tendency to form peroxides spontaneously, thereby presenting a substantial flammability risk and possibly interfering with the use of these silanes as coupling agents.
Also described in the prior art are blocked mercaptofunctional silanes, such as thiocarboxylate-functional silanes, processes for their preparation and their use in rubber compositions. A presentation on the subject was also given at the 2002 International Tire Exposition and Conference (ITEC) in Akron, Ohio. This art generally describes thiocarboxylate-functional silanes whose hydrolysable groups are derived from simple monofunctional alcohols.
The prior art also describes processes for the preparation of cyclic alkoxysilanes by reacting difunctional and trifunctional alkoxysilanes or silazanes with glycols or other diols to form cyclic monomers. These silanes however tend to self-polymerize to high viscosity polymeric materials.
The prior art also describes the kinetics and mechanisms of substitution reactions at the thiocarboxyl function in which the rate of alcoholysis of a thiol ester should be higher than the rate of thiolysis of an ester. This means that the reaction equilibrium will favor the replacement of the thiol group with the alcohol group.
The prior art does not address the use of cyclic diol-derived blocked mercapto functional silane compositions with reduced volatile organic compound (“VOC”) emissions. Accordingly, there exists a need for improved silanes.